Well it wasn't possible, but... Why not?... I just pushed version 3.3 which includes a new parameter order_by_blog when set to true it will order posts by blog ID, you can set sorting_order to asc (by default) or desc. Hope it suits your needs.

Just another short question:
Is it also possible to define a custom sort order by blog ID like [nlposts sort_by_blog=true blog_id_order=2, 1, 3] or by blog name like [nlposts sort_by_blog=true blog_name_order=NameOfBlog2, NameOfBlog1, NameOfBlog3] which results in